With a trend toward reduction in a size of cell designs to maximize integration of a semiconductor device, a space between cell pitches is also reduced. This reduction requires linear reduction in contact size. However, the reduced contact size increases contact resistance, thereby causing the semiconductor device to have a negative factor which increases power consumption and slows operating speed of the device.
In this regard, there is a need to reduce contact resistance to maximize characteristics of the device without deteriorating the advantages of the designs. Using a trench gate MOSFET is one technology that may overcome the minimized contact size by etching the silicon substrate below the surface of the silicon substrate to form the contact. This increases a total contact area that contacts silicon regions and minimizes the resistance increase.
FIG. 1 is a sectional view illustrating a trench gate MOSFET that includes a highly concentrated (P++) semiconductor substrate 40, an N+ epitaxial layer 42 formed on and/or over the substrate 40, and an N− epitaxial layer 44 formed on and/or over the N+ epitaxial layer 42. The transistor further includes a plurality of P− body regions 48 formed on and/or over the N− epitaxial layer 44. The P− body regions 48 are electrically separated from each other by trench separation regions. The trench separation regions are formed by gates 59 filled with doped polysilicon. The transistor may further include an NO epitaxial layer which is more highly concentrated than the N− epitaxial layer 44, underneath the P− body region 48 to reduce forward voltage drop of a device, N+ emitter regions 60 formed in the uppermost surface of the P− body region 48, and a contact hole 62 formed in the uppermost surface of the P− body region 48 between the N+ emitter regions 60. The transistor also includes an emitter electrode E and a collector electrode C, respectively.
Such a trench gate MOSFET has a problem of deteriorating BV characteristics of a device caused by decrease in a thickness between the bottom of P− body region and the N− epitaxial layer.